1. Field of the Invention
The present invention relates to novel, fibrous or filamentary edible proteins having certain fat particles homogeneously incorporated therein and uniformly distributed therethrough, and, more especially, relates to such fibrous food substitutes, optionally containing yet other food additives, to the method for spinning such edible proteins, and to certain apparatus for carrying out such method.
2. Description of the Prior Art
Considerable work has been done in the field of texturing various vegetable or animal proteins, in order to give them the appropriate texture, flavor and appearance which enable their use as foodstuffs for both man and animal. Extrusion and spinning are the most commonly used methods for converting crude proteins into more refined products which can be used, e.g., as meat substitutes.
By "spinning" as used herein, same is to be understood as meaning a process for the shaping of filamentary material by extrusion of a solution, a dispersion or a gel through a plate provided with orifices of small diameter, designated a spinneret or die, having a suitable shape and suitable dimensions. Threads, filaments and fibers (hereinafter simply "fibers", where practicable; usually a filament is one of continuous length, whereas a fiber is cut into shorter lengths) will denote the products obtained according to the spinning process, and a tow or bundle will denote the combination of the said filaments. Spinning offers the advantage of reproducing the fibrous nature of meats and makes it possible to obtain products which are varied in their appearance and their nutritive value. However, spinning requires the use of purified proteins such as the isolates which are powders typically comprising more than 90% of proteins. In fact, products having less than 70% of proteins cannot be directly spun.
In order to be spun, the proteins must be first converted into a protein gel; in the present text, a dispersion of protein isolates in a suitable dispersion medium, such as an alkaline solution, will be called a protein gel or a colloidal dispersion, it being possible for the said dispersion to go as far as forming a colloidal solution, depending on the type of proteins dispersed and the dispersing agent employed. The dispersion of protein isolates in a suitable dispersion medium, such as an alkaline solution, to form a protein gel or protein dispersion is well-known. See, for example, Boyer U.S. Pat. Nos. 2,730,447 and 2,682,466.
In order to produce products which simulate meat as closely as possible (meat being a term which, within the scope of the invention, encompasses both the flesh of mammals and that of birds, fish, crustaceans and other animals which man consumes in his diet), it is essential to reproduce the fibrous texture of the natural meat, to impart a good flavor to the protein fibers by adding various additives and adjuvants, and, especially, to introduce a certain amount of well-distributed fat-containing material into the said fibers.
Various methods of adding fat-containing material have been proposed to this art. For example, a process is known (compare French Pat. No. 1,048,464 and Boyer U.S. Pat. No. 2,682,466) which consists in dipping the previously coagulated protein filaments in a bath of fat. An outer coating is thus obtained on the fibers. It has been shown that this fat-containing material is not distributed inside the fibers by this process, but remains on the outside (as a sheath), giving rise to a certain heterogeneity. Furthermore, it is not possible to predetermine the amount of fat-contaning material which will be introduced, or to retain it during a subsequent processing of the fibers, such as, for example, cooking.
It too has been recommended to introduce the fat-containing material directly into the protein gel and to spin the mixture (compare Boyer U.S. Pat. No. 2,730,447). However, the homogeneity of said mixture, whether acceptable or poor, depends on the physical state of the fat-containing material. On the other hand, the prolonged contact of the fat-containing material with alkaline agents inherent in the Boyer discontinuous process effects partial saponification of the fat, altering the taste and leading to poorer digestibility of the resultant product. In addition, as the mixture of protein gel and fat-containing material is prepared in advance, and the spinning operation requires a certain period of time, the quality of the fibers thus obtained is neither constant nor is it reproducible. Also, it is to be noted that Boyer U.S. Pat. No. 2,730,447 teaches heating of the protein gel (a dispersion of protein with sodium and water) to about 160.degree. F. (70.degree. C.), followed by thorough mixing of a modifying agent such as cod liver oil, salad oil, hydrogenated animal or vegetable oil and subsequent spinning of the mixture in an acid coagulating both. Thus, the Boyer process suffers from the additional significant disadvantage of protein degradation which is caused by the combination of heat and alkaline conditions used therein. In fact, it is now known and recognized as a significant problem in the art that the heating of a protein even to around 60.degree. C. in the presence of an alkaline agent causes protein degradation. Thus, modifications in the composition of the amino acids in the protein take place, notably the disappearance of certain nutritionally valuable amino acids such as cystine, cysteine and others, and the appearance of unnatural, possible toxic amino acid derivatives such as lysinoalanine. See, for example, Cheftel et al, "Technologie et Valeur Nutritionnelle de Proteines", Revue francaise des corps gras, 23.degree. annee, No. 1, January 1976, pp. 7-9; Rham et al, Cereal Chem. 54 (2), pp. 238.gtoreq.245; and P. Besancon, "Incidences des Traitements Technologiques sur la Valeur Nutritionnelle des Proteins D'Oleagineaux", Proceedings of the 13th World Congress, International Society for Fat Research, Aug. 30-Sept. 4, 1979, Symposium 9, pp. 49-51. For example, Rham et al report that in the case of alkaline treatment of a dispersion of soybean protein at 65.degree. C. and pH 12.5 for 1.5 minutes, the disappearance of 40% of the cystine and cystine amino acids is noted.
In view of the foregoing, the present applicant proposed to prepare the protein gel in the cold state, i.e. at a temperature between about 2.degree. and 25.degree. C., so as not to degrade the protein. However, when it was attempted to introduce the fat-containing material into the cold protein gel by the method of Boyer U.S. Pat. No. 2,730,447, two difficulties were encountered: the dispersion of the fat-containing material in the gel was poor; and spinning was difficult because of clogging of the spinneret, thus making continuous operation impossible. These problems are evident from the description of an attempt to incorporate fat-containing material in a protein gel by utilizing the Boyer process at a low temperature which is entitled "COMPARATIVE EXAMPLE" and is set forth hereinafter.
Therefore, in view of the above there exists a great need in the art for fibrous, edible proteins retaining the nutritional values of the proteins from which they are prepared and containing fine, homogeneously dispersed particles of fat-containing material uniformly distributed therein, the said fat-containing material being unmodified before its incorporation and being retained during the subsequent processing and during the various uses to which said proteins are put, including human consumption.